The use of mass storage systems is as old as the use of the general purpose, stored program, digital computer. Early technologies involved magnetic drum and magnetic tape. Subsequently, magnetic disk systems of various types found widespread usage. The hardware and software of these mass storage systems are typically designed to expect a unique volume name for each defined volume within the mass storage system. This commonly takes the form of a volume name which identifies a particular magnetic tape or magnetic disk or a specific, identifiable portion thereof.
The volume name written on the mass storage medium is also written into the system storage tables. The system storage tables are used to track the location of a particular volume. An entry exists in the tables specifying the current storage bin or drive that contains a given volume. In this way, the operator and the system can each use a single volume name to identify a specific mass storage volume. In most systems, failure of the operator and/or the system to so identify a storage volume (e.g., read errors, table errors, operator errors, etc.) results in an inability to access that storage volume.
As an alternative to a name which is available to both the system and the operator, some prior art control systems developed names which are used by the system, but which are unavailable to the operator. Typically, in such an instance, the system automatically assigns a name to volumes which are to be accessed by the system, but which are not intended to be directly accessed by the operator. This approach may be adequate where the physical structure of the storage system remains unchanged. That is, systems which do not accommodate physical addition, removal or substitution of storage media such as disks or tape cassettes. However, in the situation where individual media devices, for example disks, may be repositioned, removed or added to a storage system, it is desirable that the system and the operator both have knowledge of the volume name assigned to the storage device (disk).
The identification of individual replaceable storage elements is particularly significant in a mass optical storage device which contains multiple optical volumes (disks) that must be entered into the storage system control before they can be made ready for use by the optical subsystem. In order to identify and track a volume in the system, it must have a name assigned.
It is beneficial to be able to accommodate the existence of volumes in the system without specifically assigning a name. There are also times when an assigned name of a volume becomes unknown even though the volume is physically located in the system.
For example, when a drive is allocated for a volume being entered into the system, the name may be unknown prior to the time that the label is read. Also, in the situation where the volume entered has not yet been initialized, a name is usually not assigned to it. Another such case arises when a dual-sided volume is entered into a library entry slot for the first time. In this case, even though one side of the volume may be identified, the opposite side is unknown. If a duplicate name for the volume is found to already exist in the system, the name cannot be used. If a read error occurs in the label sector of the volume, the name may be assigned but cannot be determined by the system.
These problems are particularly troublesome in the case of optical storage disks which are capable of handling far more data than comparable magnetic storage disks.